It has been constantly experienced by many that, when liquid is drained out of a sealed container, the liquid flow will slow down as vacuum builds up inside the container and eventually the flow will totally stop. This may cause inconvenience and discomfort for the user, particularly when a drinking bottle or a sport bottle is involved. For example, when using a conventional drinking bottle, the user has to stop drinking from time to time to release the built-up vacuum inside the bottle.
Different types of container caps are available in the art. U.S. Pat. No. 3,481,500 to Palma discloses a valve used with a bottle. The valve has a built-in lip which allows air to enter the bottle when vacuum is built up in the bottle due to liquid flow out of the bottle. The valve is in the form of a rubber nipple used with a nursing bottle. However, on the nursing bottle disclosed by Palma, the nipple does not seal the bottle, i.e. the passage for liquid and the passage for air are open to the atmosphere all the time. Obviously, for most applications, a container or a drinking bottle needs to be sealed for handling and preventing it from leakage and possible contamination.
U.S. Pat. No. 3,201,013 discloses a dispensing and closure cap for a liquid container. The cap has a stopper with an outlet hole which engages with a closure pin and a liquid passage. When the stopper is pushed against the bottle, the closure pin is forced into the outlet hole of the stopper, and the flow passage is blocked. When the stopper is pulled outwardly, the hole is out of touch with the closure pin, and thus, the flow passage is opened. Although the cap can seal the container and can be opened easily, this system does not have an air passage for releasing the vacuum generated due to the consumption of the liquid.
Therefore, there exists a need for a container which is sealed when not in use and which can automatically release vacuum during the consumption of the liquid content.